Heretofore, a vehicle having a smart (advanced) keyless function has been known. This type of vehicle is configured such that a user who carries an electronic key can cause a desired processing to be executed in the vehicle, simply by perform a given manipulation. For example, through the use of the smart keyless function, the user can automatically unlock a door of a vehicle simply by touching a sensor provided on a door knob (or by pushing a switch provided on the door) and then automatically lock the door simply by manipulating a manipulation section provided on the vehicle when closing the door, and can start an engine simply by pushing an engine switch.
In order to fulfill such a smart keyless function, a vehicle-mounted device mounted to the vehicle and an electronic key carried by a user are configured to be triggered by each of the above manipulations to execute a given communication processing therebetween. Then, if this communication processing (i.e., authentication) is successfully completed, a given processing will be executed in the vehicle.
Typically, in the communication processing, a first communicable distance of the electronic key with respect to the vehicle-mounted device is relatively long (e.g., several tens of meters or more), whereas a second communicable distance of the vehicle-mounted device with respect to the electronic key is relatively short (e.g., about 1 m). Therefore, the smart keyless function can be effectively enabled when a user who carries the electronic key is located around or inside the vehicle. That is, in a situation where the user (i.e., the electronic key) is located at a position away from the vehicle by a distance greater than the second communicable distance which is about 1 m, the door of the vehicle is not unlocked, for example, even if a third party touches the sensor of the door knob.
However, in recent years, the presence of a new modus operandi for vehicle theft, called “relay attack,” has been revealed. This modus operandi comprises amplifying a communication radio wave by a relay (repeater) so that the communication processing can be successfully completed between the electronic key and the vehicle-mounted device even when they are far apart from each other, thereby enabling the smart keyless function. With a view to preventing vehicle theft using the relay attack, there has been proposed, as a countermeasure against the relay attack, a technique of deactivating the smart keyless function based on a user's own will (See, for example, Patent Document 1). In the technique described in Patent Document 1, the user can temporarily deactivate the smart keyless function, for example, by performing a specific deactivation manipulation, using the electronic key.